It is commonly known that cardiac bypass surgery is a means to divert the flow of blood around arteries or veins that have become occluded or stenosed, and thus eliminate an impediment to the requirement of blood flow. A vascular graft which is a tubular device that is suitable for implantation in the body is used to reestablish or redirect the flow of blood beyond the blockage area. Surgical implantation procedures require placement of the vascular graft within the subcutaneous tissue. Vascular graft implantation requires the creation of an anatomic or subcutaneous pathway commonly called a graft tunnel. Tunneling is a required surgical step in the vascular bypass procedure for all peripheral, vascular access and extra anatomical graft locations which result in localized dissection injury to tissue. The tunnel diameter relative to the implant diameter, as well as the abrasive force exerted by the implant during insertion have a significant impact on the resultant trauma to this tissue and its healing response to both the blunt dissection of the tunnel space tissue and the vascular graft material.
It is advantageous in the clinical setting to minimize trauma to this tissue through the use of an improved tunneling technique and implant device. The conventional approach to creating a graft tunnel or space for the vascular graft is with the use of a rigid rod like device called a graft tunneler or tunneler instrument. Tunneler instruments come in varying sizes. They are usually very bulky, and require cleaning and sterilization before reuse. Improper size selection of the tunneler instrument or improper tunneling technique may result in a larger than required tunnel path through the tissue. An example of a tunneler instrument which has been designed to minimize the problem of oversizing a tissue tunnel is the Kelly-Wick tunneling set from Bard® Impra®, which is specifically designed for the implantation of vascular grafts without a tunnel sheath. Hence, this instrument is a “sheathless” system that draws a vascular graft through the dissected tissue tunnel which is created by a insertion of a rigid, bullet tipped rod through a skin incision, and forced horizontally through the subcutaneous tissue.
These type of tunneler instruments are reusable but expensive, and consequently hospitals often maintain only a limited supply of these instruments for operating room use. Since these instruments are reusable, they must be cleaned, packaged and resterilized between use. Frequently in emergency vascular surgery situations, the proper sized tunneling tip, whether it be a specific diameter, length or size, is not readily available. Consequently, the surgeon is forced to use an improper sized bullet tip (not matched to the outside diameter of the implant), or use a make-shift device. This may result in the creation of a vascular graft tunnel that is too large or too small for the graft, causing unnecessary or increased patient complications. If the tunneler instrument used creates a tunnel track that is too large for the size vascular graft being implanted, the tubular graft will not fit snugly within the tunnel and large “tunnel spaces” will exit along the entire length of the graft. This event is considered to be a major contributor to postoperative graft complications such as wound inflammation, graft material infection, and or seroma formation about the outside space of implanted graft. With an improper or “over-sized” tunnel, a significant amount of blood may pool and collect around the entire length of the implant, causing postoperative graft failure due to poor healing of the localized tissue, graft infection, and painful tissue swelling due to fluid accumulation between the dissected tissue and the implant.
Using a tunneler instrument to create a tunnel for the insertion and implantation of the vascular graft, the rigid rod like device is forcefully passed through the subcutaneous tissue horizontally between two surgically prepared incisions, until the bullet tip end is exposed at the second incision or exit wound. Once this tunneler tip is exposed, the tubular vascular graft material is placed over the bullet tipped device and tied onto the end of the indwelling tunneler rod tip with a sterile suture thread. The surgeon must carefully tie the graft to the tunneler rod with several suture knots, so as to avoid the graft from slipping off of the tunneler tip when pulled beneath the skin and into the implant position. After the vascular graft has been pulled through the dissected tissue cavity into final position, the vascular graft is then cut free at the tied end of the tunneler rod. Since the graft is exposed to the operative wound during attachment and insertion of the graft, the sterility and purity of the graft material are compromised. The process of suturing the graft to the tunneler rod and the manipulation of the graft by the surgeon further compromise the sterility of the device as a result of this “hands on” contact. Handling of the graft material during a tunneling procedure by contact with the nurse's and surgeon's gloves also increases the risk of infection by contamination from glove contact and operative wound/skin surface contact.
Another source of tissue trauma and postoperative graft complications can be created by the graft material itself due to the way the surgeon ties the graft to the tunneler. If not carefully prepared by the surgeon, part of the graft material may freely protrude over the tunneler instrument rod, forming a lip of free graft material in front of the suture tie. When the graft is forcibly pulled into and through the dissected tissue tunnel, such pulling action causes this graft material to compress, bunch up and create an abrupt or raised area in front of the suture tie which bluntly plows through the tissue, increasing the diameter of the tunnel and effectively increasing the amount of device drag in an abrasive manner, further traumatizing tissue along the entire tunnel track. This plowing action not only increases the potential for even more undesirable bleeding and tunnel track inflammation, but makes more work for the surgeon during graft insertion, particularly during long peripheral and extra anatomical bypass. This forceful graft insertion technique and risk of patient complications occurs with all commercially available vascular grafts when used with “sheathless” tunneler instruments.
“Pre-wetting” of the vascular graft material is another undesirable complication that occurs with traditional sheathless tunnelers. Since artificial vascular grafts are constructed from porous biomaterials designed to encourage rapid cell ingrowth following implantation, for example vascular grafts made from expanded polytetrafluoroethylene (PTFE), it is known that microporous graft materials should not be “pre-wetted” or “presoaked” with blood. These conditions lead to fluid leakage through the graft material once blood flow is restored within the implant, much the way a canvas tent would leak in a rain storm. If, during insertion of the graft with a traditional sheathless tunneler instrument, the tunneler tip is undersized in comparison to the outside diameter of the graft being implanted, the leading 2-5 cm length of graft material will become completely saturated with blood during the process of dragging the graft through the tissue. This is caused by the pressure placed on the tissue during graft insertion due to the initial under-sized tunnel tract. Since the thickness of the graft material adds to the outer diameter of the original bullet tip outer diameter, the leading edge of the graft material is forcibly dragged through the bleeding tissue. The pressure on the graft is controlled by the size of the tunneler tip which bluntly dissected the original tunnel space. The amount of pressure placed on the adjacent bleeding tissue and onto the graft material varies according to surgical technique and tunneler tip size selection, and thus the length and amount of graft material saturation with blood varies from patient to patient. This accounts for why some vascular graft patients unpredictably develop “seroma” formation, a serious complication of fluid accumulation around all or part of the graft material, causing moderate pain, edema and swelling of the closed wound, interstitial edema and inflammation, poor healing of the implant material, graft thrombosis and the most critical of all, systemic infection, which has an unacceptable morbidity rate. Therefore, use of a sheathless tunneler technique is not without its risk of patient complications following surgery. Such vascular graft complications may not appear for up to 30 days after patient discharge from the hospital. Hence, any surgical technique with a sheathless tunneler device which could reduce these unpredictable postoperative conditions would be clinically significant and cost effective in today's world of managed care medicine.
One example of a popular “sheathless” tunneler is the Kelley-Wick tunneling set commercially available from Bard-Impra, Tempe, Ariz. This tunneler is a one piece rod, specifically designed for the implantation of peripheral, vascular grafts (non aortic, non coronary), whereby it is the desire of the surgeon to minimize the outer tunnel space around the vascular graft implant. The device is comprised of a rigid rod that is permanently connected to a knurled handle. The rod may vary in shape and size from a straight shaft to a semicircular shaft, allowing for a variety of surgical techniques and/or placement locations. The rod is fabricated from a rigid material such as stainless steel. The rod of the instrument may terminate with a threaded on bullet tip at the opposite end to the handle. The threaded rod and bullet tip facilitates the use of different size bullet tips with a single tunneler rod to create different size tissue channels or tunnels. The Kelly-Wick tunneler is manually forced through the tissue horizontally between two incisions by the surgeon to thereby create a bluntly dissected tunnel. When tunnel dissection is completed with the bullet tip end protruding out of the distal skin incision, the vascular graft to be implanted is then attached to the tunneler tip by pushing one end of the tubular graft over the bulbous end of the bullet tip, carefully suturing and tying the end of the graft material to the bullet tip with one or two sterile suture threads. Once tied to the tunneler instrument, the vascular graft is drawn into the subcutaneous tissue channel by pulling the tunneler rod out through the first skin incision until the graft is pulled completely into the patient. When appropriately positioned between the area being bypassed, the surgeon cleanly cuts the graft away from the sutured end of the tunneler rod and tip.
While the Kelly-Wick sheathless tunneler is a popular surgical device, it has all of the previously described disadvantages. This tunneler requires that the graft be surgically positioned by pulling the graft through bluntly dissected tissue, causing further abrasion due to surface friction between the outside surface of the graft and the tissue. Further, the graft is attached to the bullet tip by sliding the graft over the tip and tying the tip and graft together. The mating of the tip and graft in this fashion creates a square edged lip at the end of the graft which tends to compress and enlarge when the graft is pulled through the tunnel, creating a “plowing” effect and causing further abrasion to the tissue wall and a larger tunnel channel. Depending on the care and preparation of the suture tying technique by the surgeon, the tunnel cavity is sometimes enlarged so that the graft does not seat snugly in the tunnel and the extra space about the graft implant would likely fill with blood and interstitial fluid.
An alternative tunneling technique uses a two (2) part tunneler instrument called a rigid “sheath tunneler,” which includes an oversized rigid metal or plastic hollow tube with a removable bullet shaped dissection tip on one end, and an internal smaller diameter indwelling rod for attaching the vascular graft material. The two part rigid sheath tunneler allows the surgeon to easily pull the vascular graft through the internal lumen of the rigid outer sheath, being substantially oversized in comparison to the outside diameter of the vascular graft. Once the graft has been pulled into the rigid sheath, the graft material is cut free from the “pull-through rod” and the subcutaneous rigid sheath is then extracted out from the tissue track and exit wound without extracting the graft. These rigid sheath tunnelers may at times be difficult to use since the rigid tubular sheaths are awkward to extract from the subcutaneous tissue due to the surface friction of the indwelling instrument. Sheath tunneler instruments require the surgeon to hold the graft in position with the pull-thru rod, a vascular clamp or gloved hands simultaneous to pulling on the rigid tubular sheath to remove it from the subcutaneous tissue.
An example of a “sheath” tunneler is the Gore tunneler which is produced by W. L. Gore and Associates, Inc. of Flagstaff, Ariz. This two part tunneler instrument is used to implant a vascular graft subcutaneously with an oversized tissue passageway. The Gore tunneler is comprised of a hollow rigid metal shaft connected to a handle with a removable bullet tip at one end of the shaft. The shaft is fabricated from stainless steel and fits into a formed handle with a center rod. The instrument is used to bluntly dissect a tunnel by forcing the bullet tipped hollow shaft through the tissue. After suture attachment of the graft material to the inner rod the vascular graft is then easily drawn through the entire length of the oversized hollow tube.
With the graft positioned in place, but still within the hollow shaft, the outer shaft tunneler must next be carefully extracted from the tissue tunnel without extracting the graft from the subcutaneous passageway. All rigid sheath tunneler devices may at times be difficult to extract from the tissue due to the compressive tension on the surrounding tissue and surface friction thereby created. The surgeon may find it necessary to use both hands to grasp the rigid hollow sheath, requiring an assistant to hold the vascular graft in position, hence, use of these type of instruments still may require significant surgical glove contact of the vascular graft during tunneling.
Another example of a two part rigid sheath tunneler is the “Scanlan” tunneler, which is similar in operative technique to the Gore device except that the rigid sheath is constructed of hard plastic and considered disposable (1 time use). The hollow shaft or tube is produced from a thicker walled, rigid plastic tube material in contrast to the thin walled stainless steel tube used with the Gore device. The Scanlan plastic hollow shaft includes a pressure fitted, removable bullet tip and an internal retractable rod. The surgeon forcibly passes the bullet shaped shaft tunneler through the tissue to create the tunnel. The bullet shaped tip of the plastic shaft is then removed and the vascular graft is attached to the inner rod with an alligator tip clamp located on the end of the pull-thru rod. Like the Gore tunneler, the Scanlan tunneler allows the graft to be easily drawn into and through the oversized hollow shaft. With two hands, the rigid plastic tube is carefully withdrawn out of the patient over the graft thru the proximal exit wound or skin incision, leaving the vascular graft within the tissue tunnel. The graft is then detached from the rod. Similar to the metal sheath tunneler instruments, the rigid plastic tube may also at times be difficult to extract from the tissue tunnel due to the compressive tension created by the bluntly dissected tissue and the surface friction created along the indwelling rigid walled shaft.
As has been previously noted, tunnelers are expensive, and consequently hospitals maintain only a limited supply of these surgical devices for hospital use. Most instruments are reusable, and are required to be washed and sterilized between use. It sometimes happens that in an emergency situation whereby disposable devices are employed, the proper sized disposable shaft component is not available. Therefore, surgeons are at times forced to use improper sized tunneling devices or alternative subcutaneous dissection items such as a gloved finger, or hemostat clamp, or a sharp surgical instrument such as a thoracic catheter trocar stylette. Thus, the resulting tunnel created by these alternative sized devices may create too large a tunnel for the vascular graft and/or unnecessary bleeding and trauma, placing the vascular implant and patient at risk.